Conductor loading system



Oct. 19, 1937. J. w. MlLNoR 2,096,401

CONDUCTOR LOADING SYSTEM Filed April 25, 193e '1 m '1 d @if d SECT/ONS OF DIFFERENT LENGT/S' 20y loaded cable circuits with terminal apparatus and Fig. 4 shows detailed diagrams illustrating 20 equal to that of the open wire lines. lar condition depending upon the 4fractional Thepresistance of openwire lines has the aplength of cable conveniently available at the end proximate value of the loaded section and also the values of the 35 'f o coils that are available. 35

- 55 coincidence vof impedance characteristics looking jl-l-W/i-@ZM 55 Patented Oct. 19, 1937 UNITED STATES PATENT OFFICE CONDUCTOR LOADING` VSYSTEMy Joseph W. Milnor, Maplewood, N. J., assigner to The Western Union Telegraph Company, New York, N. Y., a corporation of New York Application April 23, 1936, Serial No. 76,072 5 claims. (ci. 17a- 45) This invention relates to loading systems for into the loaded cable and the impedance charland line cables used for the transmission of acteristics of an open wire line over a wide f telephone and higher frequency signals and parfrequency range. These and other objects of my ticularly to a system for terminating loaded land invention will become apparent upon considera- 5 line cables so that the resistance and reactance tion of a number of examples of practice ac- 5 y of the loaded cable are substantially constant cording to the invention.

through the useful range of frequencies and cor- In the accompanying drawing, Figure 1 is a respond in value to therresistance and reactance diagram of a loaded cable terminating in midof ordinary open wire circuits. section and connected to an open Wire line; Fig.

As is well known, cable circuits are loaded in 2 is a diagram showing the impedance characl0 order to reduce attenuation of the high frequency teristics looking into the loaded cable together signals and to provide a uniform attenuation over with the impedance characteristics of an open the useful frequency rlange. This loading is wireline; Fig. 3 is a `diagram of a loaded cable usually in the form of inductance coils inserted shown in F'g. 1, but having the mid-section terat regularly spaced distances, the values of the mination supplemented in accordance with my incoils and the distances between coils being devention by additional terminal elements, e. g.: termined by the characteristics ofV the cable and in a combination of four elements; namely, fracthe frequency range which it is desired to transtional cable sections b and d and the fractional mit. It is necessary, of course, to cnnect'such loading coil a in parallel with a condenser g;

Vhaving fixedA impedance characteristics and also the principles involved in the practice of my toiunloaded open-wire lines, in which the iminvention. pedance is substantially a pure resistance with a For the purpose of explaining the principles small negative angle. At these terminal and involved in the termination of loaded cables acjunction points it is important to avoid severe cording to my invention, as illustrated in Fig. 3, 25 impedance A'discontinuities because of the objec- I shall first yshow how the impedance looking into ti'onablereflections which would, otherwise occur. the loadedv cable is derived and how the values To meet this situation it is common to adopt the of the quantities h, d, a, and g, in terms of the impedance characteristics of open wire lines as unit Values of L and C, per loading section are the standard and to design the terminal apparadetermined. Several combinations of values are 30 tus f'andvloading systems to provide an impedance developed herein, the final choice of any particui t Referring to Fig. 3, b and d are fractional loadihn the foleqlleney range Where loading 1S effective ing section lengths and g is a condenser, all eX- and Where L and C refer t0 theinductanee and pressed as fractions of full section lengths, and a capctyespectvely Per unit length 0f line A is a fractional loading coil. An expression for 4.0y system of loading designed for associated cable the jmpedanoo looking into a long loaded cable 40 conductors should have this same nominal value as measured at (1) is:

Y 2 a w/L/C f agi/m/x/l-w ,fc gcglsigtvanc component and an equivalent If and C' be each taken as unity, this expression 45 The principal objective of my invention is to becomes provide a loading system having a combination of Z1: 2 2 terminating. elements fora loaded cable such that 1/1'Tw2/4 the impedance looking into the cable will have The impedance measured at the point (2) is 50 the' above specified characteristics. Another object of my invention is to combine with a mid- I .L, 1 section termination of a loaded cable, such ad- Z Jwd 1/1-w2/4 ditional elements as will produce a substantial f 2 1 1 ZOZ and the impedance at point (3) ,Y then becomes:V Y

The foregoing table gives a range of coil sizes Which may be used to load terminal lengths (b-i-d) of cable ranging from .4 to .73 of. a section length. Below these values the element b approaches zero, while above them the element g becomes negative and the relations no longer 74500 feet and the full sized coil is 21 millihenries.

It is apparent that Within the range of values y indicatedin the table it is possible to accommopdate a large variety of fortuitous lengths of ,'f'terminating sections.

(benauwde/www4) Making s=1`w, the foregoing becomes:

Itis desired that Z4 shall be equal tothe nominal impedance ofthe loaded line for all values of s, i. e.

z4=1/L/c y With L and C each equal to unity this expression becomeszf- Z4=1, or

v*The impedance characteristics of a standard No.` 9v copper open Wire 'line including both the resistance and reactance components are shown 7 a=.597L=.0125 henry n b=.25 unitflength=1120 Y d=.37 unit length=1690' .`Q`= .118C=.0062 mf.

Where C, `.053 mf. and L=.021 henry per section length .of 4500. These curves take into account coil and line resistance. These additional fac- Equating the algebraic sum .of the coefficients of like powers of sto zero from the first three powers.

From s coefficients, a=b^+d Us? coefficients, df-=1/8a (2*) s3 coefcients, dbi+dg+bg=1/8 (3) From these equations the values of hyd," and y, in terms of a are found to V4be "Sa2 -l- 1 16a 1 1 a 'zsea-f If we assume various values of a, and solve for values of b, d, and g corresponding to a range of coilsizes a, We have:

tors r ..haverequired small `modifications in the cable lengths and coil sizes from the values originallyv determined.

The "terminating sections herein described would be used for terminating all sections of loaded cable at office terminals, open wire junctions, or patching points. 'Ihese sections would not normally be Vused other than at such locations although tWo of them back to back may be used for loading short sections of cable.

It is, of course, possible to extend the apparent length of.y cable by means of building-out condensers or cable according to Well understood practices.' While I have indicated schematically single conductors, for the purpose of description, itis to beunderstood that the indicated inductance' is divided between the two Wires of the pair of conductors, or thefffour Wires of a phantom circuit in accordance with common practice.

vIrithe foregoing description, I Vhave discloseda method of terminating sections of loaded cable in' `a three or' four element combination and which provides av resistance component that is substantially constant With respect to frequency and approximately equivalent to Ythat of the standardfxopen Wire line. At the same time the reactancer characteristic is considerably improved over that of the half-section termination. This system-has the further advantage that With a small selection of fractional coils available, .itis

possible to terminate cables having various fractional lengths and yet obtain satisfactory impedance characteristics. Cables so terminated can thus be joined to open wire sections Without impedance discontinuities or may be connected at terminals to apparatus comprising substantially pure resistance.

1. A signaling system comprising a loaded transmission line consisting of unit length cable sectionsl and unit inductance loading coils inserted at regular intervals between said sections in series with the conductors of the cable sections and a terminating system comprising, in order, a

fractional cable section, a fractional loading coil, and a second fractional cable section.

y2. A terminating system for a loaded line as in yclaim l, comprising a fractional cable section, a fractional loading coil shunted by a condenser and a fractional cable section.

3. The combination of a signaling system comprising a loaded transmission line consisting of unit length cable sections and unit inductance loading coils inserted at regular intervals between said sections in series with the co-nductors of the cable sections, said loaded line terminating in a mid-section of a unit length cable section, and a terminating system comprising, in order, a fractional cable section smaller than a half section, followed by a fractional coil and a second fractional cable section. Y

4. Atransmissio-n line comprising in sequence along its length, conductor cable sections of normal shunt capacity C, and alternate coils of normal inductance value L, an unloaded open wire line having the ratio of its inductance toits shunt capacity per unit length equal to L/C, and a terminating section for the loaded cable portion connecting the loaded and unloaded line portions, comprising a cable section of one-half unit length, and a network comprising two fractional cable section elements, and an inductance element and a capacity element connected in parallel with each other, said elements being assigned such values as to cause the impedance characteristics looking into the cable to be substantially equal to the impedance characteristics of the open wire line over a predetermined range of frequencies.

5. In a system for the transmission of telephone and higher frequency signals, comprising a transmission line having in sequence along its length, alternate inductance loading coils and cable conductor sections and ending in a midsection, a termination system for connecting said line to terminal apparatus or to an unloaded open Wire line comprising an inductance element and a capacity element connected in parallel to each other and twol fractional cable section elements, each said elements having a value less than the normal value of that element in the transmission line, such values being assigned as to cause the impedance characteristics looking into the cable to be substantially equivalent to l 

